That the tool always reloads the last code when it was left.
That is, right now the system always loads Cloak of Darkness. There’s a very plausible danger to lose progress if someone accidentally hits F5.
I suggest that the system records every last change in an internal state apart from “in browser”. And the systems always recap from there.
Also, it would be awesome if the “Load from browser” button asks “Are you sure you want to load the game saved in the browser memory?”. Because of the same, people accidentally hitting that button by error and losing progress.